Modern oil field operators demand a great quantity of information relating to the parameters and conditions encountered downhole. Among the types of information most sought is permeability, i.e., the ability of a given fluid (usually oil, water, gas, etc.) to flow through a given geologic formation. More particularly, operators desire knowledge of system permeability, i.e., the permeability of a given reservoir in situ, with the comparative stress and fracture conditions. System permeability provides a measure of the interconnectedness of the available porosity, and it is a function of fluid type, pore size and distribution, flow direction, grain size & sorting, shale content, non-connecting vugs, and fractures. It is an essential flow parameter for the characterization and production of the given reservoir. The oil and gas industry places great value on the accuracy of system permeability estimates, as they play an important role in overall reservoir management and development; i.e. economic feasibility determinations, reserve estimates, well spacing, reservoir characterization & simulation, completion designs, and secondary recovery projects.
Most commonly, the permeability of a reservoir is determined from rock samples & core analysis. However, such measurements typically occur under surface conditions, and the resulting permeability measurements are generally an order of magnitude higher than the in-situ “system permeability”. Less commonly, pressure transient analysis (e.g., drill stem testing, well shut-in testing, and diagnostic fracture injection testing (“DFIT”)) may be used to obtain permeability measurements suitable for stimulation design and reservoir simulation. Such permeability measures are performed over selected well intervals and hence may be poorly suited for a total system permeability prediction. Some researchers have proposed the use of empirical, statistical, and neural network techniques to predict formation permeability from wireline logs. However, while these techniques are effective for predicting core permeability, they do not solve for the system permeability existing in the reservoir under stress conditions.
While the invention is susceptible to various alternative forms, equivalents, and modifications, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto do not limit the disclosure, but on the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed with the described embodiments by the scope of the appended claims.